RE: PGP - non-nonrepudiation

[Carl Ellison <cme@xxxxxxx>]

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At 10:54 PM 2/5/99 -0600, Black Unicorn wrote:
>
>"But the agreement you signed with the brokerage waives the brokerage's
>liability for transactions where your keys are used."
>

That's perfectly valid.  It's the signer relinquishing his right to 
repudiate, because of a normal contract he signed with the verifier of the 
signature.  What's enforced in court is the normal contract, not some 
fiction about non-repudiation as a side effect of using digital signatures.

>I concede that non-repudiation and its definition are issues but this is
>more than a bit defeatist.  The excuse that "non-repudiation is too
>non-defined for us to try and accommodate any functionality that approaches
>it" is just silly.

I'm quite happy with the contract approach you outlined.  It's just the 
silly talk we occasionally hear about digital signatures giving 
non-repudiation -- or some certificate from a properly blessed CA giving 
non-repudiation that I contest.  There are laws (e.g., Utah) that deprive 
you of the right to repudiate if you get a certificate from some CA they 
bless -- which is enough reason, in my mind, never to get a certificate from 
such a CA.  It was, after all, the Reg E right to repudiate credit card bill 
line items that made electronic commerce thrive.

>I could apply this approach to encryption.  "Why bother to encrypt?  I have
>no idea who's at the other end.  Anyone could be a man in the middle for my
>friend.  They could sniff it with a Trojan horse on his computer.  They
>could put a video camera in his ceiling and watch his screen, or his
>keyboard."  This is effectively the approach you are taking.

In fact, I use that argument too.  There is no such thing as a man in the 
middle attack if I'm communicating with someone I don't know already.  If I 
have made contact with a stranger and some man in the middle is there, then 
I'm still communicating directly and privately with a stranger: the man in 
the middle.  I have no reason to prefer him over the other stranger, given
that I don't already have a relationship with either of them.  One might 
argue that the MITM is dishonest while the other bloke is honest, but I defy 
someone to create a protocol that tests for honesty.

>My point is that the brokerage does not now have the tools to even provide
>evidence of the signature in the first place, which- in fact- makes use of
>the signature pointless as it provides not even the slightest advance in
>non-repudiation.  Might as well just keep taking passwords or use
>handwriting analysis.

Don't run down handwriting too much.  The handwritten signature is, after 
all, a biometric.

>If you want this software to be utilized in places where it counts, which is
>of course why we are in this game, or should be, then you have to improve
>the product/protocol, not try to explain why functionality that is
>needed/useful doesn't exist.

Of course.

>Mr. Geiger points out that this functionality, or lack thereof, is not a
>consequence of the OpenPGP data structure itself.  Insofar as that is so
>this discussion is probably out of place anyhow.

Probably.

 - Carl

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+------------------------------------------------------------------+
|Carl M. Ellison         cme@xxxxxxx     http://www.pobox.com/~cme |
|    PGP: 08FF BA05 599B 49D2  23C6 6FFD 36BA D342                 |
+--Officer, officer, arrest that man. He's whistling a dirty song.-+